Effect of resonant magnetic perturbations on fast ion prompt loss in tokamaks

Fast ion prompt loss induced by resonant magnetic perturbations (RMPs) is simulated by solving Hamiltonian equations strictly in the guiding center coordinate system. Full orbit simulations show that the prompt loss rate can increase significantly in resonant regions when RMPs are added. Furthermore, the prompt loss rate is larger in the low-field side than in the high-field side in tokamak plasmas. Detailed analyses show that a number of trapped ions which lie near the center of the trapped region can be lost, because of the enhancement of radial orbit drifts induced by the resonance between RMPs and the unperturbed orbit. Meanwhile, orbit conversion from counter-passing orbit to trapped orbit occurs near the trapped-passing boundary in the low-field side, while it occurs near the co-counter boundary in the high-field side, both of which play an important role in prompt loss. Simulations also demonstrate a periodicity for orbit drifts, and the mechanism of drift periodicity results from the resonance between RMP and the equilibrium magnetic field.